A valve unit has been proposed with a housing that defines a fluid (e.g., air) flow path in communication with cylinders of an internal combustion engine. The valve unit also includes a valve coupled to the housing so as to rotate relative to the housing. The valve unit is resin-molded. (Refer to, for example, JP-2005-54627A, pages 1 to 17, FIGS. 1 to 8). This valve unit reduces weight, improves heat insulation properties, and allows for significant design freedom.
The valve unit is made by simultaneously molding the housing and the valve with the same resin material inside the molding die. The valve unit is molded with dies that abut at a seam. The valve unit is molded such that the valve is formed in the fully closed position within the housing (i.e., perpendicular to the axis of the fluid flow path). In addition, the valve shaft is provided in the molding die before the molten molding material is introduced into the die such that the valve shaft is insert-molded inside and coupled to the valve. To withdraw the molded valve unit from the dies, the dies are moved away from each other approximately parallel to the axis of the fluid flow path within the housing.
However, where the valve is a cantilever type (i.e., where the valve shaft is offset from the center of the valve), this manufacturing method can be problematic. For instance, as shown in a comparison example 1 (refer to FIGS. 12A and 12B) to be described later, the housing 101 includes upper and lower walls 102, 103. Space between the lower wall 103 and the valve shaft portion 105 is less than in the valve unit described in JP-2005-54627A. Thus, the conventional molding technique described above may not be suitable for manufacturing the valve unit with cantilevered valves. More specifically, the housing 101 and the valve 104 are molded in a state where the valve is in a fully open position. The molding die space between the lower wall 103 of the housing 101 and the valve 104 may be insufficient such that the sheet thickness is thin and the strength is reduced.
In partial response to this problem, an applicant of this application filed Japanese Application 2005-228278 (Date of Submission: Aug. 5, 2005—hereinafter referred to as “comparison example 1”) for the purpose of allowing for adequate strength of the molding die. More specifically, FIGS. 9, 12A and 12B show the valve unit installed in an intake manifold. The valve unit is provided with the housing 101, the valve 104, and the shaft portion 105. The shaft portion 105 extends axially through holes 106, 107 opened in the flow path wall surface of the housing 101 and the shaft portion 105 is rotatably supported through the bearing components 108, 109 by the housing 101. FIGS. 10A and 10B show an injection molding method for simultaneously molding the housing 101 and the valve 104 of the valve unit of the comparison example 1. The molding die is composed of at least six division slide cores 111-116. A resin material feeding device 119 feeds resin material to a first cavity corresponding to the shape of the housing 101 and a second cavity corresponding to the shape of the valve 104.
According to the injection molding method, a pellet-shaped resin material is heated and the molten resin material is injected into the molding die subject to pressures to produce a resin-molded element. Then, the resin-molded element is cooled and the dies are removed. Thereafter, the bearing components 108, 109 are press-fit between the respective through hole 106, 107 and the shaft portion 105.
When the valve 104 is in the fully open position, the “extension direction” of the valve 104 is substantially parallel to the fluid flow direction through the housing 101 (as indicated by the arrow pointing left in the housing 101 in FIG. 12A) and the axis of the fluid flow passage. Thus, as shown in FIGS. 12A and 12B, since the housing 101 and the valve 104 are molded with the valve 104 in a fully open position, first and second recessed portions 131, 132 (FIG. 9) are included for the molding die to be inserted between housing 101 and the respective side of the valve 104. This is because first and second protruding portions 121, 122 (FIGS. 10A and 10B) are provided at both sides of the valve 104 in a valve axial direction of the division slide cores 111 and 112.
In addition, in the valve unit of the comparison example 1, when the valve 104 is in the fully closed position (fully closed angle (θ)), the valve 104 is set in a slightly inclined angle relative to the axis of the fluid flow path 110 through the housing 101. The valve 104 extends downstream from the shaft portion 105 as shown in FIG. 12B. Therefore, the die used to form the valve 104 is moved in the downstream direction substantially along the axis of the fluid flow path when removing the valve unit from the dies. The recessed portions 131, 132 are included so as to extend from the vicinity of the shaft portion 105 toward the downstream side of the valve 104.
Accordingly, when the valve unit in the comparison example 1 is installed in the intake manifold and the valve 104 is in the fully open position, as shown in FIG. 9, the fluid flow from an inlet port of the housing 101 into the fluid flow path 110 passes through the shaft portion 105 of the valve 104. Thereafter, the fluid flow can separate along the front and back surfaces of the valve 104 and can flow out from an outlet port of the housing 101 to the cylinder of the internal combustion engine. However, since a part of the fluid flowing along the fluid flow path 110 flows into the first and second recessed portions 131 and 132, a disturbance can occur in the fluid flow.
Disturbance in the fluid flow can cause abnormal sounds to develop including whistling or the like or an increase in pressure loss of the fluid flow passing through the fluid flow path 110. When the pressure loss of the fluid flow increases, an intake fluid quantity (i.e., a flow quantity at the fully open position of the valve 104) introduced into the cylinder of the engine is reduced, and therefore, a required intake fluid quantity may not be achieved. As a result, the performance of the engine may be detrimentally affected.
In addition, the first and second recessed portions 131, 132 can increase the size of the housing 101. This can necessitate increased size of the valve unit as a whole and limit mounting options of the valve unit, both of which are undesirable.